To elevate data transmission reliability, wireless communication systems control and recover error of data using an Automatic Repeat Request (ARQ) scheme.
Using the ARQ scheme, a receiver sends ACK/NACK information in relation to data received, to a transmitter over an ACK/NACK channel allocated from the transmitter. The transmitter performs retransmission according to the ACK/NACK information received from the receiver. For example, upon receiving the ACK information, the transmitter recognizes that the receiver successfully receives the data, and thus sends new original data. Upon receiving the NACK information, the transmitter recognizes the data is corrupted based on the NACK information and thus retransmits the original data in response to the NACK information.
The ARQ scheme is classified to a synchronous ARQ scheme and an asynchronous ARQ scheme based on the data retransmission type.
In the asynchronous ARQ scheme, the transmitter retransmits the data by re-determining a retransmission time, a coding rate, and a resource region according to channel condition.
In the synchronous ARQ scheme, the transmitter retransmits the data using the same resource as the original data. Accordingly, the transmitter does not have to send a resource allocation message in relation to the retransmitted data. Herein, the resource allocation message includes ACK/NACK channel information for the data.
As stated above, when adopting the synchronous ARQ scheme, a base station does not send the resource allocation message with respect to the retransmitted data. In result, the ACK/NACK channel for the retransmitted data of the terminal using the synchronous ARQ scheme may collide with the ACK/NACK channel for the data of the terminal allocated the fixed resource.